Phylogenetic relationships among organisms have been demonstrated many times, and studies from a diversity of prokaryotic and eukaryotic organisms suggest a more or less gradual evolution of biochemical and physiological mechanisms and metabolic pathways. Despite different evolutionary pressures, proteins that regulate the cell cycle in yeast, nematode, fly, rat, and man have common chemical or structural features and modulate the same general cellular activity. Comparisons of human gene sequences with those from other organisms where the structure and/or function may be known allow researchers to draw analogies and to develop model systems for testing hypotheses. These model systems are of great importance in developing and testing diagnostic and therapeutic agents for human conditions, diseases and disorders.
Polycyclic aromatic hydrocarbons (PAH), such as benzo(a)pyrene (BP), are ubiquitous environmental pollutants known to cause cancer in laboratory animals. PAH induce tumors in various tissues of animal species regardless of the route of administration. Human exposure to PAH in food, air, and water is increasing, and epidemiological studies show a higher incidence of lung, skin, and bladder cancer in individuals exposed to high levels of PAH, e.g. cigarette smokers and coke oven workers.
PAH are lipophilic compounds oxidatively metabolized to epoxides, quinones, and phenols by the body's cytochrome P-450-dependent monooxygenase and epoxide hydrase. These metabolites are conjugated to more hydrophilic metabolites, most of which are secreted. However, some of the metabolites are capable of binding extensively and covalently to cellular macromolecules, such as DNA. Formation of PAH-DNA adducts appears to be an essential first step in PAH-induced neoplasia. If the cell cannot repair the damaged DNA before synthesis occurs, then replication on the damaged template can result in mutation. The two most common reactive metabolites of BP which bind to DNA are diol epoxide derivatives formed by the sequential action of the cytochrome P-450-dependent monooxygenase system and epoxide hydrase. Other PAH, such as benzanthracene, chrysene, 3-methylcholanthrene, and dimethylbenzanthracene, are also converted to very reactive diol epoxides that bind to DNA in vivo. All of these diol epoxides have a similar structure involving an epoxide ring in the bay region and have been called "bay region diol-epoxides" (Stowers and Anderson (1985) Environ. Health Perspect. 62:31-39).
The major DNA adduct formed by BP metabolites is(+)-7.beta., 8.alpha.-dihydroxy-9.alpha.,10 .alpha.-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDEI) bound to the N2 of guanine residues. Similar adduct patterns are seen in each tissue examined in mice and rabbits regardless of dose, route of administration, or time of sacrifice after dose. Differences in tissue susceptibility to PAH-induced neoplasia between different tissues may be due to the method of adduct repair. The liver, which is relatively resistant to carcinogenesis by BP, removes DNA adducts by excision repair. Lung, skin, and brain, which are more susceptible to BP-induced carcinogenesis, have little excision repair and remove DNA adducts primarily by cell turnover. If turnover rates in tissues are slow, significant levels of PAH metabolite-DNA adduct can accumulate, especially if there is continuous long-term exposure to PAH. The persistence and accumulation of DNA adducts could inhibit replication and transcription and lead to mutagenesis and carcinogenesis (Stowers and Anderson, supra).
There is growing evidence that predisposition to cancer may reside in polymorphic genes involved in carcinogen metabolism and repair. One major goal of epidemiologists is the identification of individuals who are exposed to high levels of carcinogen, carry cancer-predisposing genes, and lack protective factors. A combination of cancer-predisposing genes could be used as an intermediate risk marker rather than taking diagnosis of cancer as the endpoint. Such markers may include PAH-DNA adduct level and polymorphism in PAH-metabolizing enzymes such as the cytochrome P450 family member CYP1A1, the 4 S PAH-binding protein glutathione S-transferase (GSTM1), and cAMP-dependent protein kinase (Bhat et al. (1996) J. Biol. Chem. 271:32551-32556; and Bartsch, H. et al. (1998) Recent Results Cancer Res. 154:86-96). For example, Bartsch et al. (supra) showed that BPDE-DNA adduct levels in bronchial tissues of cigarette smokers with high CYP1A1 inducibility and inactive GSTM1 were approximately 100-fold higher than in smokers with an active GSTM 1.
Identification of genes that are expressed in response to polycyclic aromatic hydrocarbon exposure provides new diagnostic and therapeutic targets. The present invention satisfies a need in the art by providing new compositions that are useful for diagnosis, prognosis, treatment, prevention, and evaluation of therapies for cancer and its complications.